<template>
  <ul class="list">
    <li 
        class="item" 
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
    >   {{item}}
    </li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
      cities: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (tihs.timer) {
          clearTimeout(tihs.timer)
        }
        this.timer = setTimeout(() => {
         const startY = this.$refs['A'][0].offsetTop 
        const touchY = e.touches[0].clientY -79
        const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index<this.letters.length){
            this.$emit('change',this.letters[index])
          }
        },16)
      }
    },
    handleTouchEnd () {
       this.touchStatus = false
       
    }
  }
  
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
    .list
       display flex
       flex-direction column
       justify-content center
       position absolute
       top 1.58rem
       right 0
       bottom 0
       width .4rem
    .item
      line-height .44rem
      text-align center
      color $bgcolor
</style>